IS T H E E N D O
M O T O P H Y SIC S:
MAY 2017 / MOTOCROSS ACTION 85
THE GOOD NEWS IS THAT
ON LEVEL GROUND, A
MOTORCYCLE WON’T FLIP
END OVER END ON ITS OWN.
YOU HAVE TO HELP IT.
an instant deceleration of the front
wheel and fork sliders of your bike.
The motorcycle, however, continues
traveling down and forward, compressing the fork until it bottoms out.
Thanks to Newton’s law (a body in
motion will stay in motion), your body
will continue forward even after the
fork and motorcycle have decelerated. Your feet will lift off the footpegs
and your torso will slide up the seat
towards the gas cap. In a millisecond,
the majority of the motorcycle and
rider’s mass have shifted to the front
of the bike.
( 2) The somersault of doom:
Smacking the face of a bump initiates
more than just a forward weight shift.
As the fork compresses and the rear
suspension unloads, it causes the
chassis to rotate around its center of
gravity. If you anticipated this forward
rotation, you can counter it by leaning
back over the seat, yanking back on
the bars and blipping the throttle.
But if you don’t recognize the threat
soon enough, the forces will continue
( 3) Your body is your enemy:
Because the rider was caught off
guard by the sudden deceleration and
forward weight transfer, his body will
collapse to the front of the bike when
his arms buckle, shifting even more
weight forward at exactly the wrong
moment. At this point, the rear wheel
smacks the bump. The now-unweight-ed rear suspension barely compresses.
Instead of absorbing the hit, the rear
end bounces upward, adding more
velocity to your forward spin. In an
instant, your rear wheel has kicked
itself about 4 feet off the ground.